The present invention relates to dynamo electric machines, and in particular to a permanent magnet generator having a rotor including a plurality of permanent magnets generating an operative magnetic flux field.
Generally, permanent magnets generators and other like machines include an annular stator with inner winding slots containing an output winding. A capacitor may be connected in parallel with the output winding. A round circular rotor is rotatably mounted within the stator. A plurality of circumferentially distributed and permanently magnetized magnets are inserted within the outer peripheral portion of a magnetic rotor core. Generally, the core has a plurality of spaced holes or axially extended openings within which the permanent magnets are secured. The rotor structure is such that the rotor may operate at high rotational speeds, with the magnets located with regard to both the magnetic and structural limitations required for any particular design. Generally, the core structure of both the stator and the rotor are formed of a magnetic steel to form a complete interacting magnetic path for the flux created by the permanent magnets. Various patents disclose this basic structure. U.S. Pat. No. 4,517,483 which issued May 14, 1985 discloses a rather special permanent magnet structure with both circumferentially polarized magnets in one embodiment and radially polarized magnets in an alternate embodiment. Special ferrous magnetic core structures are incorporated into the rotor core structure for establishing highly saturable portions which limit the output voltage due to the saturation levels. U.S. Pat. No. 3,840,763 which issued Oct. 8, 1974 discloses a permanent magnet rotor with the magnets distributed throughout an annular core with a special distribution of the magnets creating a particular flux characteristic within the core structure without saturation thereof. U.S. Pat. No. 4,025,840 which issued May 24, 1977 discloses a permanent magnet generator with the stator specially modified with magnetic shims within the winding slots for controlling and adjusting the output power of one or more selected windings of a multiple winding, single phase permanent magnet generator.
For purposes of simplicity and conventional description, the permanent magnet generator is hereinafter referred to by the acronym PMG. The prior art has considered variations in the construction of PMG's and particular related to the arrangement of construction to control the output of the generator.
The present inventor has recognized a further problem associated with PMG's and in particular an undesirable waveshape of the voltage of the output winding. The inductance of the winding and the capacitance unit is parallel therewith creates a resonant circuit resulting in a substantial harmonic content within the fundamental output signal frequency. The result is a creation of multiple zero crossings within the fundamental frequency output which adversely affect the output current. There is a need for consideration and at least minimizing, if not eliminating, of the harmonic content to maintain and establish an optimal output voltage and current from the PMG.